Composition comprising halogenated oil

ABSTRACT

A composition that can be used as lubricant for high electric field including spark plug boots is disclosed. The composition comprises, or is produced by combining, a halogenated oil such as a perfluoropolyether, a polytrichlorofluoroethylene, a fluorosilicone, or combinations of two or more thereof; a basic thickener; and optionally an additional thickener in which the basic thickener is a metal hydroxide, a metal salt, an ammonium salt, or combinations of two or more thereof. The optional additional thickener is polytetrafluoroethylene, talc, silica, clay, boron nitride, metal soaps, titanium dioxide, polydimethylsiloxane, polyurea, polyurethane, or combinations of two or more thereof. Also provided is a spark plug boot that comprises the composition applied thereto.

FIELD OF THE INVENTION

[0001] The invention relates to a composition, which comprises ahalogenated oil and a basic thickener and can be used as a lubricant inthe presence of strong electric field and high voltage applications.

BACKGROUND OF THE INVENTION

[0002] A spark plug boot is the cover over the high voltage terminal andis typically made of a silicone rubber. A lubricant is used to aidplacement of the boot and to prevent the boot from sticking to the plug.Presently KRYTOX GPL205 (a grease containing KRYTOX GPL105perfluoropolyether oil thickened only with polytetrafluoroethylene) isused to fill the small internal space between the boot and the plug toprovide this lubrication. Likewise, similar products are marketed forthe same application. Trademarks herein are denoted by upper case names.

[0003] Under severe environment, the boot and grease are subject to ahigh voltage corona discharge. When hydrocarbon or silicone lubricantsare used, the silicone rubber boot tends to adhere to the ceramicinsulator of the plug.

[0004] A variety of types of physical barriers have been used as releaseagents in the spark plug-to-spark plug boot interface in automotiveapplications to improve the dielectric capability of the interface andto prevent the spark plug and spark plug boot from bonding to eachother. However, such techniques do not meet desired characteristics fora superior release agent.

[0005] Heretofore, greases and powders have been put in the boots, andfluorotelomer coatings have been put on spark plugs. U.S. Pat. No.5,385,686 (hereinafter referred to as “Miller et al” and incorporatedherein by reference), which contains a section diagram of the spark plugand boot assembly, discloses use of boot lubricant grease consisting ofa PTFE (polytetrafluoroethylene)-based oil and a poly(dimethylsiloxane)extender.

[0006] The desired characteristics of a superior release agent, asdisclosed in Miller et al, are to (1) provide excellent dielectriccapability, (2) prevent spark plug-to-spark plug boot bonding, (3)sustain acceptable engage/disengage forces for the interface, (4) insureno detrimental physical or chemical effects on the interface components,(5) remain operable after elevated temperatures and environmentalexposures, (6) process easily and readily, (7) be cost effective; and(8) protect the spark-plug-boot from perfluoropolyether corona dischargeproducts.

[0007] The above-described spark plug boot greases do not meet thedesired characteristics for one reason or another. Some greases tend todry up and even fall out of the interface over a period of timeresulting in poor dielectric and mechanical properties. Powders oftenhave undesired mechanical properties. Plug coatings, such asfluorotelomer, are usually much too expensive to be commerciallyutilized in automotive applications. Standard perfluoropolyether (PFPE)greases or admixtures of PFPE greases with silicones cannot protect thespark plug boot from corona discharges found in the current bootenvironment. Splitting of the boots due to the corona-induceddecomposition of PFPEs has been observed in testing and the industry.

[0008] Therefore, there is a need to develop a lubricant that canovercome the shortcomings disclosed above.

SUMMARY OF THE INVENTION

[0009] According to a first embodiment, there is provided a compositionthat comprises, consists essentially of, consists of, or is produced bycombining, a halogenated oil, a basic thickener, and optionally anadditional thickener in which the basic thickener is a metal hydroxide,a metal salt, an ammonium salt, or combinations of two or more thereof.

[0010] According to a second embodiment, there is provided a spark plugboot that comprises a composition applied thereto in which thecomposition can be the same as that disclosed above in the firstembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The term “halogenated oil” used herein referred to aperfluoropolyether, a fluorosilicone, a polytrifluorochloroethylene, orcombinations of two or more thereof.

[0012] Any perfluoropolyether, known to one skilled in the art can beused in the invention composition. A common characteristic ofperfluoropolyethers is the presence of perfluoroalkyl ether moieties.The term “perfluoropolyether” is exchangeable with “PFPE”, “PFPE oil”,“PFPE fluid”, “PFPAE”, or “perfluoropolyalkylether”, as is known to oneskilled in the art.

[0013] For example, KRYTOX available from E. I. du Pont de Nemours andCompany, Wilmington, Del. is a perfluoropolyether having the formula ofCF₃—(CF₂)₂—O—[CF(CF₃)—CF₂—O)_(s)—R_(f). In the formula, s is 2-100,inclusive and R_(f) is CF₂CF₃, a C₃ to C₆ perfluoroalkyl group , orcombinations thereof.

[0014] FOMBLIN and GALDEN fluids, available from Ausimont, Milan, Italyand produced by perfluoroolefin photooxidation, can also be used.FOMBLIN-Y can have the formula of CF₃O(CF₂CF(CF₃)—O—)_(m)(CF₂—O—)_(n)—R¹_(f). Also suitable is CF₃O[CF₂CF(CF₃)O]_(m)(CF₂CF₂O)_(o)(CF₂O)_(n)—R¹_(f). In the formulae R¹ _(f) is CF₃, C₂F₅, C₃F₇, or combinations of twoor more thereof; (m+n) is 8-45, inclusive; and m/n is 20-1000,inclusive. o is >1; (m+n+o) is 8-45, inclusive; m/n is 20-1000,inclusive; R² _(f) is CF₃, C₂F₅, or combinations thereof; t is 2-200,inclusive; (p+q) is 40-180, inclusive; and p/q is 0.5-2, inclusive

[0015] FOMBLIN-Z can have the formula ofCF₃O(CF₂CF₂—O—)_(p)(CF₂—O)_(q)CF₃ where (p+q) is 40-180 and p/q is0.5-2, inclusive.

[0016] DEMNUM fluids, available from Daiken Industries, Japan, can alsobe used. It can be produced by sequential oligomerization andfluorination of 2,2,3,3-tetrafluorooxetane, yielding the formula ofF-[(CF₂)₃—O]_(t)—R² _(f) where R² _(f) is CF₃, C₂F₅, or combinationsthereof and t is 2-200, inclusive.

[0017] Perfluoropolyethers comprising branched or straight chainperfluoroalkyl radical end groups, each of which having 3 or more carbonatoms per end group can also be used. Examples of suchperfluoropolyethers can have the formula ofC_(r)F_((2r+1))-A-C_(r)F_((2r+1)) in which each r is independently 3 to6; A can be O—(CF(CF₃)CF₂—O)_(w), O—(CF₂—O)_(x)(CF₂CF₂—O)_(y),O—(C₂F₄—O)_(w), O—(C₂F₄—O)_(x)(C₃F₆—O)_(y),O—(CF(CF₃)CF₂—O)_(x)(CF₂—O)_(y), O—(CF₂CF₂CF₂—O)_(w),O—(CF(CF₃)CF₂-O)_(x)(CF₂CF₂—O)_(y)—(CF₂—O)_(z), or combinations of twoor more thereof; preferably A is O—(CF(CF₃)CF₂—O)_(w), O—(C₂F₄—O)_(w),O—(C₂F₄—O)_(x)(C₃F₆—O)_(y), O—(CF₂CF₂CF₂—O)_(w), or combinations of twoor more thereof; w is 4 to 100; x and y are each independently 1 to 100.Specific examples include, but are not limited to,F(CF(CF₃)—CF₂—O)₉—CF₂CF₃, F(CF(CF₃)—CF₂—O)₉—CF(CF₃)₂, and combinationsthereof. In such PFPEs, up to 30% of the halogen atoms can be halogensother than fluorine, such as, for example, chlorine atoms.

[0018] Fluorosilicones suitable for use in the invention can be anyfluorocarbon containing silicone fluid. The preferred fluorosilicone isa fluorosilane, a fluorosiloxane, or combinations thereof. A suitablefluorosilicone can have the formula of R_(f)—(CH₂)_(n)—Si—R′₃ in whichR_(f) and n are the same as those disclosed above and each R′ can beindependently an alkyl group, an alkoxy group, a thioalkyl group, anamino group, an aryl group, or combinations of two or more thereof. Anexample of suitable fluorosilicone is DOW CORNING FS-1265 fluorosiliconeoil from Dow Corning, Midland, Mich.

[0019] Polytrifluorochloroethylenes suitable for use in the inventioncan have the formula of (—CCl₂CFCl—)_(s) where s is a number of 2 toabout 100. Example of suitable polytrifluorochloroethylenes areHALOCARBON oils from Halocarbon, Riveredge, N.J. The preferredpolytrifluorochloroethylene is HALOCARBON 200.

[0020] The basic thickener is one or more metal hydroxides, ammoniumsalts, and basic metal salts. The preferred basic thickeners areammonium salts, alkali metal salts, and alkaline earth metal salts suchas, for example, carbonates, bicarbonates, phosphates, carboxylates, ornitrites. The term “phosphate” used herein refers to “phosphate”,“metaphosphate”, “pyrophosphate”, or “polyphosphate”. Most preferablythe basic thickener is a basic alkali metal salt, such as sodium orpotassium carbonate or trisodium phosphate.

[0021] The amount of the basic thickener used is an amount effective toproduce a lubricant that can withstand the hostile environment under theoperating condition of an automobile spark plug. Generally, the amountcan be that which is sufficient to form a grease containing at least 0.1gram equivalents of basic thickener cation per 100 g of the compositionof the invention, preferably at least 0.26 gram equivalents of the basicthickener cation per 100 g of the composition of the invention, and mostpreferably at least 0.5 gram equivalents. For example, 0.26 gramequivalents correspond to about 6% sodium, at least about 10% potassium,or at least about 5% calcium, etc., all by weight. The upper limit forthe amount of basic thickener in the halogenated oil is determined byNational Lubricating Grease Institute (NLGI) Grade specificationrequired.

[0022] The optional additional thickeners include, but are not limitedto, PTFE (polytetrafluoroethylene), talc, silica, clay, boron nitride,metal soaps, titanium dioxide, polydimethylsiloxane, polyurea,polyurethane, or combinations of two or more thereof. These are wellknown to one skilled in the art and are commercially available.

[0023] The optional additional thickeners, if desired, in thehealogenated oil are subject to the requirement that the grease meetsGrade 000 to Grade 4 specifications, and preferably to Grade 2specifications. Greases are graded according to NLGI. All components canbe mixed together in a manner well known to those skilled in the art.

[0024] The invention composition can be produced by any means known toone skilled in the art such as, for example, mixing the compositiontogether. Because the means are well known, the discussion is omittedherein in the interest of brevity.

[0025] The present invention is further directed to the use of theinvention compositions as a spark plug boot lubricant.

[0026] According to the second embodiment of the invention, a spark plugboot having a composition applied thereto is provided. The spark plugcan be any spark plug such as an automotive spark plug. A spark plug isdisclosed in Miller et al, disclosure of which is incorporated herein byreference.

[0027] The composition can be the same as the composition disclosed inthe first embodiment of the invention.

[0028] Generally, the composition can be applied on to the wall or aportion thereof that forms the boot cavity and preferably near the endof the boot. The application can be carried out by any means known toone skilled in the art such as spraying, wiping, etc.

[0029] For example, the composition of the present invention can beplaced on a portion of the walls forming the spark plug boot cavity asdescribed by Miller et al (as described above) and preferably near theopen end of the boot. As an example of the present invention, alubricant can contain 67% by weight of a perfluoroalkylpolyether oilsuch as KRYTOX GPL105, one of the family of KRYTOX GPL (General PurposeLubricants which also includes GPL107-500) and 37% anhydrous sodiumcarbonate. KRYTOX oils and greases are available from E. I. du Pont deNemours and Company. Finely divided or micropowder forms of PTFE (alsoavailable from E. I. du Pont de Nemours and Company), talc, silica, orother additional thickener disclosed above, if desired, can also beincluded in the grease composition in amounts such that the desiredgrease consistency is obtained. Sodium carbonate can be replaced withany of the salts listed above.

[0030] While not wishing to be bound by theory, it is believed that thebasic thickeners of the present invention provide a means to removefluorine-containing degradation products, such as hydrofluoric acid,formed by high voltage discharge during use. Such reactive decompositionproducts are believed to degrade the boot and cause unwanted adhesionsand cracking in the boot assembly, complicating maintenance. Thus it canbe readily understood that greases containing less basic thickenerprovide progressively less protection.

[0031] The following examples are provided to illustrate, but are not tobe construed to unduly limit the scope of, the present invention.

Test Method

[0032] Spark Plug Boot Cracking Resistance Test

[0033] For each trial, 4 Spark plugs and lubricated boots were assembledand 15 kV RMS at 50-60 Hz applied while the assembly was maintained inan oven at 175° C. Each boot was lubricated with a nominal 0.10 g ofgrease. One boot was removed at 96 hours and the rest were removed after144 hours of continuous testing. The boots were then dissected andevaluated.

[0034] The tested boot was evaluated on a scale of 0 (best) to 5 (worst)with the evaluation criteria shown in Table 1. Each grease sample wasevaluated with three boots and the ratings were averaged. An evaluationof 3.7 or lower is required, preferably 2.5 or lower after the 144 hoursexposure. TABLE 1 Evaluation Criteria Rating No crazing or cracking, asin an untested boot. 0 Rating Heavy surface crazing but relatively veryminor shallow 1 cracks in the upper portion of the tower seal. Level ofcrazing/cracking is very minor and not considered to be a significantopportunity for failure. Rating Moderate amount of relative shallowcracking just above the 2 tower seal area. Rating Moderate amount ofdeep cracking in upper portion of tower 3 seal; very small shallowcracks throughout the tower seal; a few large cracks at the extreme endof the boot tower seal. Rating Heavy to severe deep cracking in theupper portion of the 4 tower seal and very small shallow cracksthroughout the tower seal area. Rating Severe deep cracking in upperportion of tower seal and 5 significant amount of medium depth cracksthroughout tower seal, some cracks/splits at bottom of tower seal (endof boot).

EXAMPLES

[0035] Greases were prepared by conventional methods well known to thoseskilled in the art of grease making. Basically, with excellent mixing,one added thickener to a halogenated oil until the desired NLGI Grade ofhardness was obtained (in this case grade 2). Different thickeners andadditives were incorporated into the test greases, as shown in the key.The normal practice was to prepare a grease for which the penetrationwas adjusted by additions of either oil or thickener and mixing using a3-roll mill with a 0.0010 inch (0.00254 cm) gap until the final resultis an NLGI #2 grease. Compositions were described in weight percent.

Example 1

[0036] A NLGI Grade 2 grease was prepared by the conventional methoddescribed above from KRYTOX GPL105 (67%) using anhydrous sodiumcarbonate (Na₂CO₃, 33%, EM Science Brand from VWR, Gibbstown N.J.) asthickener.

Examples 2-7 and Comparative Examples A-C

[0037] The following Examples and Comparative Examples were prepared asin Example 1, using sodium carbonate, potassium carbonate, trisodiumphosphate, IGACOR DSSG (disodium sebacate from Ciba Specialty Chemicals,Tarrytown, N.Y.), and PTFE (any micropowder of medium size 15 mm or suchas those available from E. I. du Pont de Nemours and Company) as shownin Table 2. TABLE 2 Grease Compositions. Ex. # PFPE Oil (%) Thickener(s)(%) Penetration* Examples 1 KRYTOX GPL105 (67) Na₂CO₃ (33) 287 2 KRYTOXGPL105 (74.6) K₂CO₃ (25.4) 268 3 KRYTOX GPL105 (56) Na₃PO₄ (44.0) 290 4KRYTOX GPL105 (67) Na₂CO₃ (16.5), 279 PTFE (16.5) 5 KRYTOX GPL105 (69)Na₂CO₃ (7.75), 275 PTFE (23.25) 6 KRYTOX GPL107-500 IGACOR DSSG (21.3)287 (78.7) 7 KRYTOX GPL105 (76.9) IGACOR DSSG (23.1) 272 ComparativeExamples A KRYTOX GPL105 (75) PTFE (25) 287 B KRYTOX GPL107-500 PTFE(21.5) 290 (78.5) C KRYTOX GPL105 (75) PTFE (20), 287 IGACOR DSSG (5)

[0038] Test results using the Spark Plug Boot Cracking Resistance Testare shown in Table 3. TABLE 3 Cracking Test Data 96 Hour 144 Hour 144Hour Cation g Individual Individual Rating equivalent/ Ex. # RatingRatings Average 100 g Grease Examples 1 (Trial 1) 1 1, 1, 1 1 0.62 1(Trial 2) 2.3 2, 2.3, 2.3 2.2 0.62 2 1 1, 3, 3 2.3 0.62 3 2.3 2, 2, 3.32.43 0.80 4 1 1, 1.5 1.2 0.31 5 2 2.3, 2.3, 2.6 2.4 0.15 6 3.6 3.6, 3.63.6 0.19 7 2.3 3.6, 3.6, 3.6 3.6 0.17 Comparative Examples A (Trial 1)3.8 4, 4, 4 4 0 A (Trial 2) 4 4, 4, 4 4 0 B 3.8 4, 4, 4 4 0 C 4 4, 5, 44.3 0.04

[0039] As can be seen in the above Tables, the lubricant of the presentinvention, utilizing a combination of perfluoroalkylpolyether and alkalimetal salt in a grease, greatly reduces spark-plug-boot cracking duringsevere service.

What is claimed is:
 1. A composition comprising or produced by combininga halogenated oil, a basic thickener, and optionally an additionalthickener wherein said halogenated oil is a perfluoropolyether, afluorosilicone, a polytrifluorochloroethylene, or combinations of two ormore thereof and said basic thickener is a metal hydroxide, a metalsalt, an ammonium salt, or combinations of two or more thereof.
 2. Acomposition according to claim 1 wherein said halogenated oil is saidperfluoropolyether and is CF₃—(CF₂)₂—O—[CF(CF₃)—CF₂—O]_(s)—R_(f),CF₃O[CF₂CF(CF₃)—O—]_(m)(CF₂—O—)_(n)—R¹ _(f), F—[(CF₂)₃—O]_(t)—R² _(f),CF₃O(CF₂CF₂—O—)_(p)(CF₂—O)_(q)CF₃,CF₃O[CF₂CF(CF₃)O]_(m)(CF₂CF₂O)_(o)(CF₂O)_(n)—R¹ _(f), or combinations oftwo or more thereof; s is 2-100, inclusive; R_(f) is CF₂CF₃, a C₃ to C₆perfluoroalkyl group, or combinations thereof; R¹ _(f) is CF₃, C₂F₅,C₃F₇, or combinations of two or more thereof; (m+n) is 8-45, inclusive;(m+n+o) is 8-45, inclusive; m/n is 20-1000, inclusive; o is >1; R² _(f)is CF₃, C₂F₅, or combinations thereof; t is 2-200, inclusive; (p q) is40-180, inclusive; and p/q is 0.5-2, inclusive.
 3. A compositionaccording to claim 2 wherein said perfluoropolyether isCF₃—(CF₂)₂—O—[CF(CF₃)—CF₂—O]_(s)—R_(f).
 4. A composition according toclaim 1 wherein said basic thickener is an ammonium salt, an alkalimetal salt, an alkaline earth metal salt, or combinations of two or morethereof.
 5. A composition according to claim 2 wherein said basicthickener is an ammonium salt, an alkali metal salt, an alkaline earthmetal salt, or combinations of two or more thereof.
 6. A compositionaccording to claim 1 wherein said basic thickener is ammonium carbonate,ammonium bicarbonate, ammonium phosphate, ammonium carboxylate, alkalimetal carbonate, alkali metal bicarbonate, alkali metal phosphate,alkali metal carboxylate, alkaline earth metal carbonate, alkaline earthmetal bicarbonate, alkaline earth metal phosphate, alkaline earth metalcarboxylate, or combinations of two or more thereof.
 7. A compositionaccording to claim 2 wherein said basic thickener is ammonium carbonate,ammonium bicarbonate, ammonium phosphate, ammonium carboxylate, alkalimetal carbonate, alkali metal bicarbonate, alkali metal phosphate,alkali metal carboxylate, alkaline earth metal carbonate, alkaline earthmetal bicarbonate, alkaline earth metal phosphate, alkaline earth metalcarboxylate, or combinations of two or more thereof.
 8. A compositionaccording to claim 1 wherein said basic thickener is sodium carbonate,trisodium phosphate, potassium carbonate, tripotassium phosphate, orcombinations of two or more thereof.
 9. A composition according to claim2 wherein said basic thickener is sodium carbonate, trisodium phosphate,potassium carbonate, tripotassium phosphate, or combinations of two ormore thereof.
 10. A composition according to claim 3 wherein said basicthickener is sodium carbonate, trisodium phosphate, potassium carbonate,tripotassium phosphate, or combinations of two or more thereof.
 11. Acomposition according to claim 1 wherein said additional thickener ispolytetrafluoroethylene, talc, silica, clay, boron nitride, metal soaps,titanium dioxide, polydimethylsiloxane, polyurea, polyurethane, orcombinations of two or more thereof.
 12. A composition according toclaim 6 wherein said additional thickener is polytetrafluoroethylene,talc, silica, clay, boron nitride, metal soaps, titanium dioxide,polydimethylsiloxane, polyurea, polyurethane, or combinations of two ormore thereof.
 13. A composition according to claim 10 wherein saidadditional thickener is polytetrafluoroethylene, talc, silica, clay,boron nitride, metal soaps, titanium dioxide, polydimethylsiloxane,polyurea, polyurethane, or combinations of two or more thereof.
 14. Acomposition comprising or produced by combining a halogenated oil, abasic thickener, and optionally an additional thickener wherein saidhalogenated oil is a perfluoropolyether, a fluorosilicones, apolytrifluorochloroethylene, or combinations of two or more thereof;said basic thickener is an ammonium salt, an alkali metal salt, analkaline earth metal salt, metal hydroxide, or combinations of two ormore thereof; said additional thickener is polytetrafluoroethylene,talc, silica, clay, boron nitride, metal soaps, titanium dioxide,polydimethylsiloxane, polyurea, polyurethane, or combinations of two ormore thereof.
 15. A composition according to claim 14 wherein saidhalogenated oil is said perfluoropolyether and isCF₃—(CF₂)₂—O—[CF(CF₃)—CF₂—O]_(s)—R_(f),CF₃O[CF₂CF(CF₃)—O—]_(m)(CF₂—O—)_(n)—R¹ _(f), F—[(CF₂)₃—O]_(t)—R² _(f),CF₃O(CF₂CF₂—O—)_(p)(CF₂—O)_(q)CF₃,CF₃O[CF₂CF(CF₃)O]_(m)(CF₂CF₂O)_(o)(CF₂O)_(n)—R¹ _(f), or combinations oftwo or more thereof; s is 2-100, inclusive; R_(f) is CF₂CF₃, a C₃to C₆perfluoroalkyl group, or combinations thereof, R¹ _(f) is CF₃, C₂F₇,C₃F₇, or combinations of or two or more thereof; (m+n) is 8-45,inclusive; o is >1; (m+n+o) is 8-45, inclusive; m/n is 20-1000,inclusive; R² _(f) is CF₃, C₂F₅, or combinations thereof; t is 2-200,inclusive; (p+q) is 40-180, inclusive; and p/q is 0.5-2, inclusive; andsaid basic thickener is ammonium carbonate, ammonium bicarbonate,ammonium phosphate, ammonium carboxylate, alkali metal carbonate, alkalimetal bicarbonate, alkali metal phosphate, alkali metal carboxylate,alkaline earth metal carbonate, alkaline earth metal bicarbonate,alkaline earth metal phosphate, alkaline earth metal carboxylate, orcombinations of two or more thereof.
 16. A composition according toclaim 15 wherein said halogenated oil isCF₃—(CF₂)₂—O—[CF(CF₃)—CF₂—O)_(s)—R_(f) and said basic thickener issodium carbonate, sodium triphosphate, potassium carbonate, potassiumtriphosphate, or combinations of two or more thereof.
 17. A compositioncomprising or produced by combining a perfluoroppolyether, a basicthickener, and optionally an additional thickener wherein saidperfluoropolyether is CF₃—(CF₂)₂—O—[CF(CF₃)—CF₂—O]_(s)—R_(f); said basicthickener is sodium carbonate, sodium triphosphate, potassium carbonate,potassium triphosphate, or combinations of two or more thereof, and saidadditional thickener is polytetrafluoroethylene, talc, silica, clay,boron nitride, metal soaps, titanium dioxide, polydimethylsiloxane,polyurea, polyurethane, or combinations of two or more thereof.
 18. Aspark plug having applied thereto a composition as recited in any one ofclaims 1 to 17.